Manufacture of electromagnetic devices



April 14, 1964 s. D. vlGREN ETAL 3,128,537

MANUFACTURE OFv ELECTROMAGNETIC DEVICES Filed June 25, 1959 2 Sheets-Sheet 1 April 14, 1964 s. D. vlGREN ETAL MANUFACTURE 0F ELECTROMAGNETIC DEVICES 2 Sheets-Sheet 2 Filed June 25, 1959 Wjwwf ffy/2 United States Patent Otice 3,128,537 Patented Apr. 14, 1964 3,128,537 MANUFACTURE F ELECTRSMAGNETIC DEVHCES Sten Daniel Vigren, 16-18 Mose Backetorg, Stockholm, Sweden; Per Harry Elias Claessen, 4 Sportstugevagen, Danderyd, Sweden; and Rolf Aibin Zander, 15 Ivar Vidfamnesgatan, Stockholm, Sweden Filed .lune 25, 1959, Ser. No. 822,949 Claims priority, appiication Sweden .lune 26, 1958 6 Claims. (Cl. 29-1555) The present invention relates to the manufacture of electromagnetic devices and more specically to the adjustment of the distances between surfaces on certain parts of the magnetic structure, for instance the distance between the pole faces defining an air gap in polarized control devices.

It is an object of the invention to provide a method by which the adjustment of said distances can be carried out in a simple manner and with a high accuracy so that exact distances can be attained although the dimensions of the parts may vary within comparatively wide limits. By the method according to the invention a considerable reduction of the costs in large scale manufacture of electromagnetic devices can be obtained.

In accordance with the invention at least one distance member or gauge block is placed between said surfaces and then the parts carrying said surfaces are subjected to pressure so that the parts and the distance member are brought into Contact with each other. The dimensions of the distance member in the direction of the pressure is so chosen in relation to the springing back of the parts that the desired distance between the surfaces is obtained when the pressure ceases and the distance member is removed.

The invention will be described more in particular with reference to the accompanying drawings which illustrate the application of the invention to the manufacture of a telephone receiver.

FIGURES 1 to 3 show a telephone receiver in three different elevations, FIGURES 1 and 3 showing the receiver partly in section.

FIGURES 4 to 6 and 7 to 9 illustrate two diiferent ways of applying the invention to the adjustment of the air gap in the magnetic circuit of the telephone receiver.

FIGURES 10 to 12 illustrate the application of the invention to the assembling of the magnetic circuit of the telephone receiver.

FlGURE 13 is a diagram showing the length of the air gap after the adjustment as a function of the length of the airgap before the adjustment.

The telephone receiver shown in FIGURES 1 to 3 comprises two pole pieces 1 and 2, four spacing tubes 3 6, an armature 7, two bolts or rivets 8 and 9, a permanent magnet 10, a coil with a coil form 11, a base plate 12, a diaphragm 13, a connecting link 14 between the armature and the diaphragm, a disc 15, damping members of foamed plastic or similar material 17-19, a spacing ring 20 and a cover 21 with sound openings 22.

The armature 7 is suspended in two arms clamped between the spacing tubes 3-4 and 5-6 and the pole pieces 1 and 2 by means of the bolts or rivets 8 and 9. The spacing tubes and pole pieces are also secured to the base plate 15 by means of bolts or rivets 8*-9. The disc 15 is clamped between pole piece 2 and base plate 12. The armature 7 is surrounded by coil 11.

The damping members of foamed plastic or similar material 17 and 13 are xed between diaphragm 13 and disc 15 as will be seen from FIGURES 1 and 3. Ths said material has a damping effect on the air current produced by the diaphragm when this vibrates, that is the damping material reduces the resonant sharpness (Q value) of the diaphragm as well as of two acoustic cavities, one defined by the diaphragm, base plate 12 and disc 15 and the other formed between disc 15 and a casing (not shown on the drawing) in which the magnetic system is mounted as shown in our co-pending application Serial No. 648,056, filed March 27, 1959. The damping effect can be adjusted in simple manner by pushing the damping member 13 more or less into the aperture in the disc 15, the edge of said aperture having tabs or the like 16 which x the damping member in the desired position.

The ring 19 which is also made of foamed plastic or the like reduces the resonant sharpness of the acoustic cavity dened by the cover 20 and diaphragm 13.

The coil form 11 preferably has two arms 23 and 24 shown in FIGURES 2 and 3. vMetal pegs 25 and 26 are attached to those ends of said arms which are located remotest from the coil form. The pegs 25 and 26 serve as connecting means for connecting the winding of the coil to external connections to the telephone receiver. Arms 23 and 24- are provided with grooves 2S, so that a light ray directed along line X (FGURE 2) can illuminate the air gaps between the armature and the poles which facilitates the adjustment of the armature to a central position in the air gap and also facilitates the iinal checking of the air gap of the telephone receiver. The illumination is preferably effected in a so called profile projector which produces an enlarged picture of the air gap. The said adjustment of the armature can be performed for instance by inserting a key (metal strip having grooves corresponding to the thickness of the armature) between the magnet and one of the bolts or rivets 3-9.

In order that the telephone receiver shall operate satisfactorily it is required that the air gaps between the armature and the pole faces of the pole pieces are given exact dimensions in the direction of movement of the armature. As appears from the gures these air gaps are determined by the height of the magnet, the length of the poles and the thickness of the armature. Assuming that the magnet is ground with a tolerance of 10.03 mm., the poles likewise with a tolerance of i003 mm. and the armature is rolled with a tolerance of 10.05 mm., it will be realized that the combined length of the air gaps can vary by 2 (0.03-1-003+0.03-}-0.05)=0.28 mm. This means that each air gap can vary by maximum 0.14 mm. Thus, although very close tolerances have been maintained, the variations in the length of the air gaps becomes too large to give a uniform product in large scale manufacture. If it is desired to increase the tolerances for the purpose of reducing the manufacturing costs, e.g. by omitting grinding of the pole faces, the variations are further increased.

These difficulties are avoided by the method in accordance with the present invention which will now be explained with reference to FIGURES 4 to 6. According to the invention the dimensions of the magnet and the poles and the armature shall be so chosen that when the said parts have been assembled into a unit as shown in FIGURES 1 to 3 the air gaps between the armature and the poles are somewhat too large. This is illustrated in FIGURE 4. The procedure according to the invention is illustrated in FIGURE 5. As shown in this figure the telephone receiver is clamped between two cheeks 29 and 30 located opposite to the ends of the magnet. A distance member 31 is then inserted between one pole and the armature. The pole pieces 1 and 2 are then subjected to pressure by means of cheeks 32 and 33 so that the poles, the armature and the distance member are brought into contact with each other. Then the pressure is removed from cheeks 32 and 33 and the distance member 31 is removed. The poles will now spring back somewhat l; s whereby the desired distance between the armature and the poles is attained as illustrated in FIGURE 6.

Practical tests have shown that the amount of springing back reaches a constant value when the compression exceeds a certain amount. This appears from the diagram in FIGURE 13. The abscissa in the diagram indicates the length of the air gap in millimetres before the compression, and the ordinate indicates a length of the air gap in millimetres after the poles have been compressed and the pressure removed. In the tests the results of which are shown in the diagram, a distance member with a thickness of 0.2 mm. was used and the applied pressure amounted to 600 kg.

If the pole pieces are made of annealed iron with low carbon content and have a thickness of 2 mm. and are so arranged that the distance between the magnet and those sides which are facing the magnet, is 6 mm., the said constant value is obtained at a compression of at least 0.3 mm. The amount of the springing back then becomes 0.14 mm. This applies to the combined compression and springing back of both poles. The height of the magnet, the height of the spacing tubes, the length of the poles and the thickness of the armature shall be so chosen that the least compression in the example mentioned above shall be 0.3 mm. The largest compression thus becomes 0.3 -{-0.28=0.58 mm. The practical tests have shown however that the compression can be relatively large, for instance in average 0.6 mm. Therefore the tolerances of said parts need not be as close as stated in the example above. Thus, the grinding of the poles can be omitted and the tolerances of the magnet and the armature can be comparatively large whereby the costs of manufacture are correspondingly reduced.

The initial dimensions of the magnet, the poles and the armature can also be so chosen that when said parts are assembled the air gaps are very small or even zero as shown in FIGURE 7. Before the pole pieces are screwed or riveted together, the distance member 31 is inserted between one pole and the armature, and then pressure is applied to the pole pieces by means of cheeks 29 and 30 as shown in FIGURE 8. After the pressure and the distance member have been removed the correct air gap is obtained as shown in FIGURE 9. Even in this case the thickness of the distance member must be so chosen with regard to the springing back of the poles that the desired distance is obtained between the poles.

The procedure according to the invention can also be applied to the putting together of the magnetic system by means of screws or rivets in the manner illustrated in FIGURES 10 to 12.

After the parts of the telephone receiver except the cover 21, diaphragm i3, `and the damping member I9 and ring have been placed in correct position with respect to each other and the bolts or rivets 8 9 have been inserted, the base plate 12 is placed on fixed support 45, whereafter a pressure die 34 is placed on pole piece I. This die 34 is provided with openings 35 and 36 for said bolts or rivets. The die 3d is also formed with shoulders in such manner that it can press down those parts of pole piece I which are located outside the magnet along lines y and z in FIGURE 12. During this compression the center portion 37 of pole piece 1 should be kept pressed against the magnet by means of a pressure piston 38 which is actuated by means of a spring 39 resting against plate 40 and exerts a pressure of such magnitude that pole piece 1 is kept in contact with the magnet during the compression procedure. Assuming that the parts 8--9 are screw bolts, the pressure die 34 is removed after completing the compression procedure, and nuts are applied to the bolts and tightened so that the various parts are properly securely to each other. This is made possible by the invention since the pole piece I springs back only to a small extent after the pressure has been removed, and the springing back is practically the same whether the pole piece has been compressed to the least or largest l extent corresponding to the manufacturing tolerances of the parts. In this case the spacing tubes 3-6 serve as distance members.

Assuming that parts 8 9 are rivets, riveting tools 41 and 42 are inserted in the holes 35 and 36 in the pressure die 34.

If necessary a third fastening bolt or rivet 43 can be provided for securing the various parts to each other. Then the magnet is preferably provided with a groove through which bolt 4.3 extends.

When applying the invention for large scale manufacture of for instance telephone receivers the necessary pressure is produced in any known manner suitable for the purpose, e.g. by means of hydraulic devices, mechanical lever systems or the like.

In electromagnetic devices which are not polarized, e.g. ordinary electromagnetic relays, the length of only one air gap is to be adjusted. In this case the armature and the pole coacting with the armature are pressed against each other so that the necessary mechanical deformation is produced in the armature or the pole in order that a predetermined air gap shall be obtained the length of which is independent of the magnitude of the compression within the tolerance range of the different parts of the relay.

What is claimed is:

l. A method in the manufacttue of a polarized electromagnetic device which includes permanent magnet means and two pole pieces of magnetic material connected to poles at opposite sides of the permanent magnet means and having end portions carrying pole faces facing each other to form an air gap of predetermined length and an armature positioned between said pole pieces and having an end extending into said air gap, said method comprising the steps of: manufacturing the permanent magnet means and the pole pieces to specied dimensions within given tolerance limits and connecting the permanent magnet means and the pole pieces in an assembly, said dimensions being such that after assembling the permanent magnet means and the pole pieces the length of the air gap between said pole faces is slightly different from said predetermined length; inserting at least one spacing member between the armature and one of said pole faces; applying pressure to the pole pieces to move them into close contact with the poles of the permanent magnet means and to move said pole faces into contact with said spacing member and armature under deformation of the pole pieces; and removing said pressure and said spacing member, the size of said spacing member being so chosen in relation to the dimensions of the permanent magnet means the armature, the pole pieces and the predetermined length of the air gap that after removal of the pressure and the spacing means the said end portions of the pole pieces spring back to such extent that the distance between said pole faces becomes substantially equal to said predetermined length.

2. A method in the manufacture of a polarized electromagnetic device which includes a magnetic structure comprising permanent magnet means and two pole pieces connected to poles at opposite ends of the permanent magnet means and having end portions carrying pole faces facing each other to form an air gap of a predetermined length and an armature positioned between said pole pieces and having an end extending into said air gap, said method comprising the steps of: manufacturing the permanent magnet means and the pole pieces to specified dimensions within given tolerance limits and arranging the pole pieces in the desired position in relation to the permanent magnet means, said dimensions being such that after arranging the pole pieces in the desired posiktion in relation to the permanent magnet means the length of the air gap between said pole faces will be somewhat larger than said predetermined length; inserting spacing means in said air gap between said armature and one pole piece face, said spacing means together with said armature having a thickness somewhat smaller than said predetermined length of the air gap; pressing the pole pieces in close contact with the poles of the permanent magnet means and simultaneously applying pressure to bend said end portions of the pole pieces to such extent that each of said pole faces are moved towards and into contact with the spacing means and armature; and removing said pressure and spacing means, the size of said spacing means together with said armature being so chosen in relation to said dimensions of the permanent magnet means and the pole pieces and the said predetermined length of the air gap that after removal of the pressure the pole pieces spring back whereby the distance between the pole faces becomes substantially equal to said predetermined length.

3. A method in the manufacture of a polarized electromagnetic device which includes permanent magnet means, two pole pieces connected to poles at opposite ends of the permanent magnet means and having end portions carrying pole faces facing each other to form an air gap of predetermined length, and an armature having a part extending into said air gap and located at equal distances from said pole faces, said method comprising the steps of: manufacturing the permanent magnet means, the pole pieces and the armature to specified dimensions within given tolerance limits and arranging the permanent magnet means, the pole pieces and the armature in the desired position in relation to one another, said dimensions being such that after said arrangement the length of the air gap between the pole faces is somewhat larger than said predetermined length; inserting spacing means between the armature and at least one of the pole faces, said spacing means having such thickness that the combined thickness of the spacing means and the armature is somewhat smaller than said predetermined length of the air gap; keeping the pole pieces in close contact with the poles of the permanent magnet means and simultaneously applying pressure to said end portions of the pole pieces to bend each end portion towards the other to the extent permitted by the armature and the spacing means; and removing the pressure and spacing means, said spacing means having such size in relation to the dimensions of the permanent magnet means, the pole pieces and the armature and said predetermined length of the air gap that after removal of the pressure the end portions of the pole pieces spring back to such extent that the distance between the pole faces becomes substantially equal to said predetermined length and the end of said armature remains substantially centrally spaced between said pole piece faces.

4. A method in the manufacture of a polarized electromagnetic device which includes permanent magnet means having two pole surfaces which are substantially parallel to each other, two pole pieces connected, one connected to each pole surface of the permanent magnet means, and having portions extending away from the permanent magnet means, said extending portions having ends bent towards each other to define an air gap of predetermined length therebetween, and an armature positioned between said pole pieces and having an end extending into said air gap; said method comprising the steps of: manufacturing the permanent magnets means, the pole pieces and the armature to specified dimensions Within given tolerance limits, said dimensions being such that after assembling the permanent magnet means and the pole pieces the length of the air gap between said ends of the pole pieces would be somewhat smaller than said predetermined length; positioning the permanent magnet means and the armature between the pole pieces and inserting spacing means between the armature and said bent end of atleast one of the pole pieces, said spacing means having such size that the combined thickness of the armature and the spacing means is somewhat larger than said predetermined length of the air gap; applying pressure to those parts of the pole pieces which are located adjacent the pole surfaces of the permanent magnet means to press the pole pieces in close contact with said pole surfaces, thereby causing the extending portions of each pole piece to be bent backwardly due to the presence of said spacing means between the armature and the ends of the pole pieces; securing the pole pieces in relation to the permanent magnet means; and removing the pressure and said spacing means, the size of said spacing means being so chosen in relation to the dimensions of the permanent magnet means and the pole pieces and the armature and the said predetermined length of the air gap that after removal of the spacing means the bent ends of the pole pieces will spring back to such extent that the distance between said ends becomes substantially equal to said predetermined length.

5. A method as claimed in claim 1 wherein said pole pieces further have two side portions extending laterally in opposite directions from the permanent magnet means, and clamping means connecting said side portions of one pole piece with corresponding side portions of the other pole piece, and said method further comprises the steps of: assembling the permanent magnet means, the pole pieces and the clamping means in the desired positions With respect to each other without securing the clamping means to the pole pieces; inserting spacing members between said side portions of the pole pieces before the said step of pressing the pole pieces in close contact with the poles of the permanent magnet means; applying a pressure to said side portions of one pole piece while pressing the pole pieces in contact with the permanent magnet means to press said pole piece side portions towards the corresponding side portions of the other pole piece to the extent permitted by said spacing members; securing the clamping means to the pole pieces; and removing the pressure.

6. A method as claimed in claim 5 in which pressure is applied to those portions of the pole pieces which are in contact with the poles of the permanent magnet means at the same time as said pressure is applied to said side portions.

References Cited in the le of this patent UNITED STATES PATENTS 1,384,209 OToole July 12, 1921 2,193,886 Schulz Mar. 19, 1940 2,336,611 Hill et al. Dec. 14, 1943 2,362,006 Herzog Nov. 7, 1944 2,388,953 Coombs Nov. 13, 1945 2,449,428 Timmons Sept. 14, 1948 2,511,114 Lavery June 13, 1950 2,549,165 Brackenbury et al Apr. 17, 1951 2,582,942 Baker Jan. 22, 1952 2,692,918 Berger Oct. 26, 1954 2,754,569 Kornei July 17, 1956 2,961,497 Heppner Nov. 22, 1960 3,002,057 Vigren et a1 Sept. 26, 1961 FOREIGN PATENTS 634,422 Germany Aug. 27, 1936 469,004 Great Britain July 16, 1937 497,074 Canada Oct. 20, 1953 

1. A METHOD IN THE MANUFACTURE OF A POLARIZED ELECTROMAGNETIC DEVICE WHICH INCLUDES PERMANENT MAGNET MEANS AND TWO POLE PIECES OF MAGNETIC MATERIAL CONNECTED TO POLES AT OPPOSITE SIDES OF THE PERMANENT MAGNET MEANS AND HAVING END PORTIONS CARRYING POLE FACES FACING EACH OTHER TO FORM AN AIR GAP OF PREDETERMINED LENGTH AND AN ARMATURE POSITIONED BETWEEN SAID POLE PIECES AND HAVING AN END EXTENDING INTO SAID AIR GAP, SAID METHOD COMPRISING THE STEPS OF: MANUFACTURING THE PERMANENT MAGNET MEANS AND THE POLE PIECES TO SPECIFIED DIMENSIONS WITHIN GIVEN TOLERANCE LIMITS AND CONNECTING THE PERMANENT MAGNET MEANS AND THE POLE PIECES IN AN ASSEMBLY, SAID DIMENSIONS BEING SUCH THAT AFTER ASSEMBLING THE PERMANENT MAGNET MEANS AND THE POLE PIECES THE LENGTH OF THE AIR GAP BETWEEN SAID POLE FACES IS SLIGHTLY DIFFERENT FROM SAID PREDETERMINED LENGTH; INSERTING AT LEAST ONE SPACING MEMBER BETWEEN THE ARMATURE AND ONE OF SAID POLE FACES; APPLYING PRESSURE TO THE POLE PIECES TO MOVE THEM INTO CLOSE CONTACT WITH THE POLES OF THE PERMANENT MAGNET MEANS AND TO MOVE SAID POLE FACES INTO CONTACT WITH SAID SPACING MEMBER AND ARMATURE UNDER DEFORMATION OF THE POLE PIECES; AND REMOVING SAID PRESSURE AND SAID SPACING MEMBER, THE SIZE OF SAID SPACING MEMBER BEING SO CHOSEN IN RELATION TO THE DIMENSIONS OF THE PERMANENT MAGNET MEANS THE ARMATURE, THE POLE PIECES AND THE PREDETERMINED LENGTH OF THE AIR GAP THAT AFTER REMOVAL OF THE PRESSURE AND THE SPACING MEANS THE SAID END PORTIONS OF THE POLE PIECES SPRING BACK TO SUCH EXTENT THAT THE DISTANCE BETWEEN SAID POLE FACES BECOMES SUBSTANTIALLY EQUAL TO SAID PREDETERMINED LENGTH. 